And you really should stop being so sure about your affirmation, save if you're actually working in the field.
I can't find any sources saying that reactor fuel can't form a critical mass. If you have some please give them.
You may or may not believe my education in the matter (here, I'm just an anonymous avatar... In fact, I don't even
have an avatar...) but I would like to assert that to get nuclear-fuel grade material into nuclear-bomb grade material is a bit of a difficult process (hence the fuss over various nations <cough>Iran</cough> having centrifuges and the like).
Getting enough fission-supporting isotope into a small-enough area, with less than a certain amount of other contaminants (non-fissile isotypes, waste nuclear products, what's left of the coolant, what's there of the stuff they've dumped into the core to try and prevent the event) from a mere melt-down to the extent of getting to enough mass at bomb-grade densities (and, as has been pointed out, various nuclear weapons may also require explosive charges to compress the fissile material even further, as part of the effort to get the required nuclear explosion going on) is not exactly as unlikely as all the atoms of oxygen in the room suddenly deciding they all want to be packed at one side of it but not at the other, but mathematically very much with the same meta-order of magnitude or so.
There are some good authoritative on-line sources, but there's enough places out there with "proof" of that thoroughly disproved cold fusion method, perpetual motion machine building instructions and things such as the Time Cube, so if your Bachelors has given you your current opinion I can't see you taking anything I'd show you any more seriously.
(To address the ninja posts from Thief^ and Tellemurius, I'd be happy if we were talking about Japan, but there's only so much info us armchair newshounds can relay before it gets to "Yup, it still looks bad." I think a quick diversion down one particularly detailed (albeit heated) discussion about a still-developing occurrence should be relevent, and at least keep us interested until the Next Big Thing. Or whatever develops from the current situation. I'd also find it slightly morbid and distracting if someone was giving twice-daily body-counts, given that we can't do anything to have made anybody not die or especially to make sure that people as yet not found to be dead could be found alive, but if there was no other news to speak of I could see that dominating this. Along with the "OMG! WTF! Before and after pictures here! Video here!" and suchlike that is going to rumble along as long as there's new stuff to add following this general meme.)